EP0412408B1 - Electrically conductive polymer and its use as orientation layer in liquid crystal switches and display devices - Google Patents

Electrically conductive polymer and its use as orientation layer in liquid crystal switches and display devices Download PDF

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EP0412408B1
EP0412408B1 EP90114643A EP90114643A EP0412408B1 EP 0412408 B1 EP0412408 B1 EP 0412408B1 EP 90114643 A EP90114643 A EP 90114643A EP 90114643 A EP90114643 A EP 90114643A EP 0412408 B1 EP0412408 B1 EP 0412408B1
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liquid
polymer
formula
electrically conductive
integer
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German (de)
French (fr)
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EP0412408A3 (en
EP0412408A2 (en
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Claus Dr. Escher
Hans-Rolf Dr. Dübal
Michael Dr. Feldhues
Takamasa Harada
Gerhard Dr. Illian
Thomas Dr. Mecklenburg
Mikio Murakami
Dieter Dr. Ohlendorf
Karl Dr. Pampus
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Hoechst AG
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Hoechst AG
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    • GPHYSICS
    • G02OPTICS
    • G02FOPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333Constructional arrangements; Manufacturing methods
    • G02F1/1337Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
    • G02F1/133711Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by organic films, e.g. polymeric films
    • CCHEMISTRY; METALLURGY
    • C09DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09KMATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00Liquid crystal materials
    • C09K19/04Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
    • C09K19/38Polymers
    • CCHEMISTRY; METALLURGY
    • C09DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09KMATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K2323/00Functional layers of liquid crystal optical display excluding electroactive liquid crystal layer characterised by chemical composition
    • C09K2323/02Alignment layer characterised by chemical composition
    • GPHYSICS
    • G02OPTICS
    • G02FOPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/137Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
    • G02F1/139Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
    • G02F1/141Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent using ferroelectric liquid crystals

Definitions

  • ferroelectric liquid crystals serve as switching and display medium (FLC displays) are described, for example, in US Pat. No. 4,367,924. They contain a layer of a ferroelectric liquid-crystalline medium (FLC), which is enclosed on both sides by electrically insulating layers, electrodes and boundary plates, usually glass plates. They also include one polarizer when in guest host mode and two polarizers when operating in birefringence mode.
  • the electrically insulating layers are intended to prevent electrical short circuits between the electrodes and the diffusion of ions from the glass of the boundary plates into the liquid-crystalline layer.
  • At least one and preferably both of the insulating layers serve as an orientation layer, which brings the liquid-crystalline material into a configuration in which the molecules of the liquid-crystalline layer lie with their longitudinal axes parallel to one another, and in which the smectic planes are arranged perpendicular or obliquely to the orientation layer.
  • orientation layer which brings the liquid-crystalline material into a configuration in which the molecules of the liquid-crystalline layer lie with their longitudinal axes parallel to one another, and in which the smectic planes are arranged perpendicular or obliquely to the orientation layer.
  • FLC displays can therefore be switched bistably. The switching times are in the range of ⁇ s and the shorter the higher the spontaneous polarization of the liquid-crystalline material used.
  • FLC displays Compared to the previously used liquid crystal displays, which are generally not ferroelectric, FLC displays have the particular advantage that the multiplex ratio, ie. H. the maximum number of lines that can be controlled in the time-sequential method (“multiplex method”) is very much larger than in the known non-ferroelectric displays.
  • a disadvantage of FLC displays can, however, result from the fact that a display that has been in one of the two stable states for a long time (standing picture) is very difficult, i. H. with a very high amplitude or very long pulse duration of the applied voltage is to be switched to the other state, that is to say shows a pronounced optical hysteresis.
  • liquid crystal elements which contain a film of polythiophene or polypyrrole derivatives on at least one substrate surface.
  • Electrically conductive polymers that contribute in oxidized form in dipolar aprotic solvents are room temperature soluble and which are derived from a monomer of formula (II) where at least one of the two radicals R3 and R4 is an alkoxy group and the other is optionally (C1-C6) alkyl or hydrogen, have already been described in DE-A 3 717 668, DE-A 3 628 895 and DE-A 3 736 114. The presentation, stability and electrical conductivity of the various positively doped polymers were also examined at this point.
  • Electrically conductive polymers of the formula (I) with a (positive) degree of doping of 10 to 30% are particularly suitable for use in liquid crystal switching and display elements, the degree of doping being the ratio of the electrical charge (m) of the polymer to the number of monomer units from which it is built.
  • the undoped polymers have only a negligibly low electrical conductivity, and highly doped polymers (polymeric radical cations) are mostly unstable or difficult to access.
  • Such conductive polymers are particularly preferably used as a component of the orientation layers in FLC displays in which n in the formula (I) is an integer from 4 to 30 and m is an integer from 1 to 9, very particularly preferred for n is one integer from 4 to 10 and for m an integer from 1 to 4.
  • conductive polymers in which X in the formula (I) denotes a sulfur atom and which are used as the anion (Y ⁇ ) BF - 4th , PO 3- 4th , SO 2- 4th , HSO - 4th , F ⁇ and / or Cl ⁇ included.
  • the orientation layer preferably contains 30 to 100% by weight of the conductive polymer of the general formula (I).
  • Other components that can be used are both electrically conductive materials and non-conductive substances, in particular organic polymers.
  • the orientation layer in the liquid crystal switching and display element contains, in addition to a polymer of the formula (I), a non-conductive polymer such as, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, polyvinyl acetate, polyvinyl chloride, Poly-vinyl methyl ether, poly-vinyl methyl ketone, poly-maleic anhydride, poly-styrene, poly-N-vinyl carbazole, poly-N-vinyl pyrrolidone, poly vinyl pyridine, poly methacrylate, poly methyl methacrylate, poly acrylonitrile, polyacetaldehyde, poly acrolein, Poly-ethylene oxide, poly-tetrahydrofuran, aliphatic polyester, poly-carbonate, poly-butyl isocyanate, natural rubber, poly-urethane, methyl cellulose, ethyl cellulose, cellulose triacetate or poly-
  • the orientation layer can also contain other conductive polymers.
  • one of the orientation layers may consist of an electrically conductive polymer, while the other is an electrically insulating layer.
  • An FLC display is subjected to a sequence of bipolar voltage pulses (Fig. 1a), and that in each case follows an "reset pulse" R, which is so large that the display switches in any case, an inverse test pulse T. If the Voltage of the test pulse (V t ) high enough, the display switches in the opposite direction to the reset pulse, which causes the display to flash.
  • the ordinate is the intensity (in volts; which is proportional to the transmission) and the abscissa is the electrical field strength (in volts / ⁇ m).
  • Fig. 2 shows a comparison of the hysteresis curve obtained by the method explained above of a known display, in which the electrodes are isolated from the FLC by an orientation layer (Fig. 2a), and a display according to the invention, in which two orientation layers made of rubbed conductive polymer in are in direct contact with the FLC (Fig. 2b).
  • Fig. 2a shows a comparison of the hysteresis curve obtained by the method explained above of a known display, in which the electrodes are isolated from the FLC by an orientation layer (Fig. 2a), and a display according to the invention, in which two orientation layers made of rubbed conductive polymer in are in direct contact with the FLC (Fig. 2b).
  • the extensive suppression of hysteresis in the latter case is clearly visible.
  • a 2% nitromethane solution of an electrically conductive polymer with the following structural formula, where n is 5 or 6, is by a spin coating process at 1500 revolutions / minute on a 1 mm thick Glass substrate, which had previously been provided with a transparent electrode, spun on for 30 seconds.
  • the substrate and the layer of the solution deposited thereon are annealed at 120 ° C. in a drying cabinet in order to drive the solvent by distillation.
  • a polymer layer with a layer thickness of 100 nm is obtained, which is then rubbed lightly twice in the same direction using a grinder.
  • a homogeneous, slightly bluish polymer layer with a thickness of 100 nm and a specific electrical conductivity of 8.0 x 10 -3 S / cm is obtained.
  • the solution is applied in the same way as described in Example 1 on a glass substrate which has previously been provided with a transparent electrode. After annealing for one hour at 180 ° C., the layer thickness is 150 nm.
  • a liquid crystal cell with A 2 ⁇ m thick liquid crystal layer is produced by aligning the substrates in the same manner as in Example 1.
  • the cell is filled with the commercially available ferroelectric liquid crystal mixture ®Felix 002 (manufacturer: Hoechst AG). A good bistability is found.
  • the liquid crystal switching element shows almost no optical hysteresis. 77% are measured as the optical transparency of the orientation layer at a light wavelength of 550 nm.

Description

Schalt- und Anzeigeelemente, bei denen ferroelektrische Flüssigkristalle als Schalt- und Anzeigemedium dienen (FLC-Displays), werden beispielsweise in US-A 4,367,924 beschrieben. Sie enthalten eine Schicht aus einem ferroelektrischen flüssigkristallinen Medium (FLC), die beiderseitig von elektrisch isolierenden Schichten, Elektroden und Begrenzungsscheiben, üblicherweise Glasscheiben, eingeschlossen ist. Außerdem enthalten sie einen Polarisator, wenn sie im Guest-Host-Mode, und zwei Polarisatoren, wenn sie im Doppelbrechungs-Mode betrieben werden. Die elektrisch isolierenden Schichten sollen elektrische Kurzschlüsse zwischen den Elektroden und die Diffusion von Ionen aus dem Glas der Begrenzungsscheiben in die flüssigkristalline Schicht verhindern. Ferner dient mindestens eine und vorzugsweise beide der isolierenden Schichten als Orientierungsschicht, die das flüssigkristalline Material in eine Konfiguration bringt, bei der die Moleküle der flüssigkristallinen Schicht mit ihren Längsachsen parallel zueinander liegen, und in der die smektischen Ebenen senkrecht oder schräg zur Orientierungsschicht angeordnet sind. In dieser Anordnung gibt es für die FLC-Moleküle zwei mögliche und gleichwertige Orientierungen, in die sie durch pulsartiges Anlegen eines elektrisches Feldes gebracht werden können. Sie verharren jeweils in der zuletzt erzeugten Orientierung, auch wenn das Feld abgeschaltet oder das Display kurzgeschlossen wird. FLC-Displays sind also bistabil schaltbar. Die Schaltzeiten liegen im Bereich von µs und sind um so kürzer, je höher die spontane Polarisation des verwendeten flüssigkristallinen Materials ist.Switching and display elements in which ferroelectric liquid crystals serve as switching and display medium (FLC displays) are described, for example, in US Pat. No. 4,367,924. They contain a layer of a ferroelectric liquid-crystalline medium (FLC), which is enclosed on both sides by electrically insulating layers, electrodes and boundary plates, usually glass plates. They also include one polarizer when in guest host mode and two polarizers when operating in birefringence mode. The electrically insulating layers are intended to prevent electrical short circuits between the electrodes and the diffusion of ions from the glass of the boundary plates into the liquid-crystalline layer. Furthermore, at least one and preferably both of the insulating layers serve as an orientation layer, which brings the liquid-crystalline material into a configuration in which the molecules of the liquid-crystalline layer lie with their longitudinal axes parallel to one another, and in which the smectic planes are arranged perpendicular or obliquely to the orientation layer. In this arrangement there are two possible and equivalent orientations for the FLC molecules, into which they can be brought by applying an electric field in a pulsed manner. They remain in the orientation they were last created, even if the field is switched off or the display is short-circuited. FLC displays can therefore be switched bistably. The switching times are in the range of µs and the shorter the higher the spontaneous polarization of the liquid-crystalline material used.

Gegenüber den bisher verwendeten Flüssigkristalldisplays, die in der Regel nicht ferroelektrisch sind, haben FLC-Displays insbesondere den Vorzug, daß das erreichbare Multiplexverhältnis, d. h. die maximale Zahl der im zeitlich sequentiellen Verfahren ("Multiplex-Verfahren") ansteuerbaren Zeilen, sehr viel größer ist als bei den bekannten nicht- ferroelektrischen Displays.Compared to the previously used liquid crystal displays, which are generally not ferroelectric, FLC displays have the particular advantage that the multiplex ratio, ie. H. the maximum number of lines that can be controlled in the time-sequential method (“multiplex method”) is very much larger than in the known non-ferroelectric displays.

Ein Nachteil von FLC-Displays kann sich jedoch daraus ergeben, daß ein Display, das sich längere Zeit in einem der beiden stabilen Zustände befunden hat (stehendes Bild), nur sehr schwer, d. h. mit sehr hoher Amplitude oder sehr langer Pulsdauer der angelegten Spannung in den anderen Zustand umzuschalten ist, also eine ausgeprägte optische Hysterese zeigt. Bei bildhaften Anzeigen führt das dazu, daß ein längere Zeit eingeschriebenes Bild im Nachfolgebild schemenhaft als sog. "Geisterbild" zu erkennen ist. Diese Erscheinung der optischen Hysterese ist um so stärker ausgeprägt, je höher die spontane Polarisation des FLC-Materials ist. Da andererseits die Schaltzeit von FLC-Materialien zur spontanen Polarisation umgekehrt proportional ist, wird ein wichtiger Vorteil der FLC-Displays durch diese Hysterese wieder zunichte gemacht. Die Ursache dieses Phänomens ist bisher nicht eindeutig geklärt; es gibt Anzeichen dafür, daß ionische Verunreinigungen im FLC dafür verantwortlich sind.A disadvantage of FLC displays can, however, result from the fact that a display that has been in one of the two stable states for a long time (standing picture) is very difficult, i. H. with a very high amplitude or very long pulse duration of the applied voltage is to be switched to the other state, that is to say shows a pronounced optical hysteresis. In the case of pictorial advertisements, this leads to the fact that a picture which has been inscribed for a long time can be recognized in the following picture as a so-called "ghost picture". This phenomenon of optical hysteresis is more pronounced the higher the spontaneous polarization of the FLC material. On the other hand, since the switching time of FLC materials for spontaneous polarization is inversely proportional, an important advantage of the FLC displays is nullified by this hysteresis. The cause of this phenomenon has not yet been clearly clarified; there is evidence that ionic contaminants in the FLC are responsible.

Es wurde bereits in der prioritätsälteren, nicht-vorveröfftentlichten DE-A 3 843 228 vorgeschlagen, die beschriebene Erscheinung der optischen Hysterese in FLC-Displays dadurch stark zu vermindern oder zu unterdrücken, daß mindestens eine der Elektroden in unmittelbaren elektrischen Kontakt mit dem flüssigkristallinen Medium gebracht wird.It was already proposed in the older, unpublished DE-A 3 843 228 to greatly reduce or suppress the described appearance of optical hysteresis in FLC displays by bringing at least one of the electrodes into direct electrical contact with the liquid-crystalline medium becomes.

In der prioritätsälteren, nicht vorveröffentlichten europäischen Patentanmeldung 353 760 (benannte Vertragsstaaten DE, FR, GB, IT) sind Flüssigkristallelemente vorgeschlagen, die auf mindestens einer Substratfläche einen Film aus Polythiophen- oder Polypyrrolderivaten enthalten.In the older, not prepublished European patent application 353 760 (designated contracting states DE, FR, GB, IT), liquid crystal elements are proposed which contain a film of polythiophene or polypyrrole derivatives on at least one substrate surface.

Es wurde nun überraschenderweise gefunden, daß man die optische Hysterese in FLC-Displays besonders effektiv dadurch unterdrücken kann, daß man ein Flüssigkristall-Schalt- und -Anzeigeelement verwendet, das ein ferroelektrisches flüssigkristallines Medium, zwei Elektroden, mindestens einen Polarisator, zwei transparente Trägerplatten und mindestens eine Orientierungsschicht enthält, wobei mindestens eine der Orientierungsschichten in unmittelbarem elektrischen Kontakt mit der zugehörigen Elektrode steht und diese Orientierungsschicht ein elektrisch leitfähiges Polymer enthält, das aus wiederkehrenden Einheiten der Formel (I) besteht:

Figure imgb0001

wobei

H oder geradkettiges oder verzweigtes Alkyl oder Alkoxy mit 1-16 C-Atomen oder Halogen,
geradkettiges oder verzweigtes Alkoxy mit 1-16 C-Atomen oder Halogen
X
S oder NH
Y⁻
BF - 4
Figure imgb0002
, PF - 6
Figure imgb0003
, PO 3- 4 
Figure imgb0004
, AsF - 6
Figure imgb0005
, SbCl - 6
Figure imgb0006
, SO 2- 4 
Figure imgb0007
, HSO - 4
Figure imgb0008
, Alkyl-SO - 3
Figure imgb0009
, Perfluoralkyl-SO - 3
Figure imgb0010
, Aryl-SO - 3
Figure imgb0011
, F⁻ oder Cl⁻,
n
eine ganze Zahl von 4 bis 100 und
m
eine ganze Zahl von 1 bis 30 bedeuten.
It has now surprisingly been found that optical hysteresis in FLC displays can be suppressed particularly effectively by using a liquid crystal switching and display element which comprises a ferroelectric liquid crystalline medium, two electrodes, at least one polarizer, two transparent carrier plates and contains at least one orientation layer, at least one of the orientation layers being in direct electrical contact with the associated electrode and this orientation layer containing an electrically conductive polymer which consists of repeating units of the formula (I):
Figure imgb0001

in which
H or straight-chain or branched alkyl or alkoxy with 1-16 C atoms or halogen,
straight-chain or branched alkoxy with 1-16 C atoms or halogen
X
S or NH
Y⁻
BF - 4th
Figure imgb0002
, PF - 6
Figure imgb0003
, PO 3- 4th
Figure imgb0004
, AsF - 6
Figure imgb0005
, SbCl - 6
Figure imgb0006
, SO 2- 4th
Figure imgb0007
, HSO - 4th
Figure imgb0008
, Alkyl-SO - 3rd
Figure imgb0009
, Perfluoroalkyl-SO - 3rd
Figure imgb0010
, Aryl-SO - 3rd
Figure imgb0011
, F⁻ or Cl⁻,
n
an integer from 4 to 100 and
m
is an integer from 1 to 30.

Elektrisch leitfähige Polymere, die in oxidierter Form in dipolar aprotischen Lösungsmitteln bei Raumtemperatur löslich sind und die sich von einem Monomer der Formel (II) ableiten

Figure imgb0012

wobei zumindest einer der beiden Reste R³ und R⁴ eine Alkoxygruppe bedeuten und der andere gegebenenfalls (C₁-C₆)-Alkyl oder Wasserstoff ist, wurden bereits in den DE-A 3 717 668, DE-A 3 628 895 und DE-A 3 736 114 beschrieben. Auch die Darstellung, die Stabilität und elektrische Leitfähigkeit der verschiedenen positiv dotierten Polymere wurden an dieser Stelle untersucht.Electrically conductive polymers that contribute in oxidized form in dipolar aprotic solvents Are room temperature soluble and which are derived from a monomer of formula (II)
Figure imgb0012

where at least one of the two radicals R³ and R⁴ is an alkoxy group and the other is optionally (C₁-C₆) alkyl or hydrogen, have already been described in DE-A 3 717 668, DE-A 3 628 895 and DE-A 3 736 114. The presentation, stability and electrical conductivity of the various positively doped polymers were also examined at this point.

Für die Anwendung in Flüssigkristall-Schalt- und Anzeigelementen sind elektrisch leitfähige Polymere der Formel (I) mit einem (positiven) Dotierungsgrad von 10 bis 30 % besonders geeignet, wobei der Dotierungsgrad das Verhältnis von elektrischer Ladung (m) des Polymers zur Anzahl der Monomereinheiten, aus denen es aufgebaut ist (n), angibt. Die undotierten Polymere besitzen nur eine vernachlässigbar kleine elektrische Leitfähigkeit, hochdotierte Polymere (polymere Radikalkationen) sind zumeist instabil oder schwer zugänglich.Electrically conductive polymers of the formula (I) with a (positive) degree of doping of 10 to 30% are particularly suitable for use in liquid crystal switching and display elements, the degree of doping being the ratio of the electrical charge (m) of the polymer to the number of monomer units from which it is built. The undoped polymers have only a negligibly low electrical conductivity, and highly doped polymers (polymeric radical cations) are mostly unstable or difficult to access.

Besonders bevorzugt werden solche leitfähigen Polymere als Bestandteil der Orientierungsschichten in FLC-Displays eingesetzt, bei denen in der Formel (I) n eine ganze Zahl von 4 bis 30 und m eine ganze Zahl von 1 bis 9 bedeuten, ganz besonders bevorzugt wird für n eine ganze Zahl von 4 bis 10 und für m eine ganze Zahl von 1 bis 4.Such conductive polymers are particularly preferably used as a component of the orientation layers in FLC displays in which n in the formula (I) is an integer from 4 to 30 and m is an integer from 1 to 9, very particularly preferred for n is one integer from 4 to 10 and for m an integer from 1 to 4.

Bevorzugt werden ferner leitfähige Polymere eingesetzt, bei denen X in der Formel (I) ein Schwefelatom bedeutet, und die als Anion (Y ⁻ ) BF - 4

Figure imgb0013
, PO 3- 4 
Figure imgb0014
, SO 2- 4 
Figure imgb0015
, HSO - 4
Figure imgb0016
, F⁻ und/oder Cl ⁻ enthalten.It is also preferred to use conductive polymers in which X in the formula (I) denotes a sulfur atom and which are used as the anion (Y ⁻) BF - 4th
Figure imgb0013
, PO 3- 4th
Figure imgb0014
, SO 2- 4th
Figure imgb0015
, HSO - 4th
Figure imgb0016
, F⁻ and / or Cl ⁻ included.

Bevorzugterweise enthält die Orientierungsschicht 30 bis 100 Gew.-% des leitfähigen Polymers der allgemeinen Formel (I). Als andere Komponenten kommen sowohl elektrisch leitfähige Materialien wie auch nicht leitende Stoffe, insbesondere organische Polymere, in Frage.The orientation layer preferably contains 30 to 100% by weight of the conductive polymer of the general formula (I). Other components that can be used are both electrically conductive materials and non-conductive substances, in particular organic polymers.

Die Orientierungsschicht enthält im Flüssigkristall-Schalt- und -Anzeigeelement in einer weiteren Ausführungsform der Erfindung neben einem Polymer der Formel (I) ein nichtleitfähiges Polymer wie z.B. Poly-vinylformal, Poly-vinylacetal, Poly-vinylbutyral, Poly-vinylacetat, Poly-vinylchlorid, Poly-vinylmethylether, Poly-vinylmethylketon, Poly-maleinsäureanhydrid, Poly-styrol, Poly-N-vinylcarbazol, Poly-N-vinylpyrrolidon, Poly-vinylpyridin, Poly-methylacrylat, Poly-methylmethacrylat, Poly-acrylnitril, Polyacetaldehyd, Poly-acrolein, Poly-ethylenoxid, Poly-tetrahydrofuran, aliphatische Polyester, Poly-carbonat, Poly-butylisocyanat, natürliches Gummi, Poly-urethan, Methylcellulose, Ethylcellulose, Cellulosetriacetat oder Poly-methylsiloxan. Die Orientierungsschicht kann aber auch weitere leitfähige Polymere enthalten.
Insbesondere bei großflächigen Displays kann es zur Vermeidung von Kurzschlüssen zweckmäßig sein, daß eine der Orientierungsschichten aus einem elektrisch leitfähigen Polymer besteht, während die andere eine elektrisch isolierende Schicht darstellt.
In a further embodiment of the invention, the orientation layer in the liquid crystal switching and display element contains, in addition to a polymer of the formula (I), a non-conductive polymer such as, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, polyvinyl acetate, polyvinyl chloride, Poly-vinyl methyl ether, poly-vinyl methyl ketone, poly-maleic anhydride, poly-styrene, poly-N-vinyl carbazole, poly-N-vinyl pyrrolidone, poly vinyl pyridine, poly methacrylate, poly methyl methacrylate, poly acrylonitrile, polyacetaldehyde, poly acrolein, Poly-ethylene oxide, poly-tetrahydrofuran, aliphatic polyester, poly-carbonate, poly-butyl isocyanate, natural rubber, poly-urethane, methyl cellulose, ethyl cellulose, cellulose triacetate or poly-methyl siloxane. The orientation layer can also contain other conductive polymers.
In particular in the case of large-area displays, in order to avoid short circuits, it may be expedient for one of the orientation layers to consist of an electrically conductive polymer, while the other is an electrically insulating layer.

Die Verminderung der optischen Hysterese ist um so ausgeprägter, je höher die elektrische Leitfähigkeit der Polymere ist. Ihre spezifische Leitfähigkeit soll daher in der Richtung senkrecht zu ihrer Ebene mindestens 10⁻⁵ Siemens · m⁻¹ und ihre Leitfähigkeit mindestens 100 Siemens · m⁻² betragen.The higher the electrical conductivity of the polymers, the more pronounced the reduction in optical hysteresis. Their specific conductivity should therefore be at least 10⁻⁵ Siemens · m⁻¹ in the direction perpendicular to their plane and their conductivity should be at least 100 Siemens · m⁻².

Die Erfindung wird auch durch die anliegende Zeichnung näher erläutert:The invention is also explained in more detail by the attached drawing:

Das Phänomen der optischen Hysterese ist in Figur 1 dargestellt.The phenomenon of optical hysteresis is shown in Figure 1.

Ein FLC-Display wird einer Folge von bipolaren Spannungspulsen unterworfen (Fig. 1a), und zwar folgt jeweils auf einen "Reset-Puls" R, der so groß ist, daß das Display in jedem Fall schaltet, ein inverser Testpuls T. Ist die Spannung des Testpulses (Vt) groß genug, so schaltet das Display in umgekehrter Richtung wie beim Reset-Puls, was zu einer blinkenden Anzeige des Displays führt. Die Mindestspannung (kritische Spannung des Testpulses) Vt c (Fig. 1b), die zum Schalten durch den Testpuls nötig ist, ist dabei von der Vorgeschichte des Schaltens des Displays abhängig. Ist die Ausgangssituation so, daß die Testpulse zu klein zum Schalten sind, so daß eine statische Anzeige vorliegt, so führt die Erhöhung der Testpulsspannung Vt erst bei relativ hohen Werten V c  t2

Figure imgb0017
(Fig. 1b) zu einer schaltenden, d. h. blinkenden, Anzeige (Fig. 1a, oben). Reduziert man ausgehend von V c  t2
Figure imgb0018
die Höhe des Testpulses (Fig. 1a unten), so schaltet das Display weiter (blinkende Anzeige), und erst bei Reduzierung der Höhe des Testpulses deutlich unterhalb V c  t2
Figure imgb0019
schaltet der Testpuls das Display nicht mehr (V c  t1
Figure imgb0020
), und die Anzeige wird wieder statisch. Diese "optische Hysterese" ist in Fig. 1b idealisiert dargestellt (Tr steht für die optische Transmission, Vt ist die Spannung des Testpulses).An FLC display is subjected to a sequence of bipolar voltage pulses (Fig. 1a), and that in each case follows an "reset pulse" R, which is so large that the display switches in any case, an inverse test pulse T. If the Voltage of the test pulse (V t ) high enough, the display switches in the opposite direction to the reset pulse, which causes the display to flash. The minimum voltage (critical voltage of the test pulse) V t c (Fig. 1b), which is necessary for switching by the test pulse, depends on the history of switching the display. If the initial situation is such that the test pulses are too small to switch, so that there is a static display, the increase in the test pulse voltage V t only leads to relatively high values V c t2
Figure imgb0017
(Fig. 1b) to a switching, ie flashing, display (Fig. 1a, above). Starting from V c t2
Figure imgb0018
the level of the test pulse (Fig. 1a below), the display switches on (flashing display), and only when the level of the test pulse is reduced significantly below V c t2
Figure imgb0019
the test pulse no longer switches the display (V c t1
Figure imgb0020
), and the display becomes static again. This "optical hysteresis" is idealized in Fig. 1b (Tr stands for optical transmission, V t is the voltage of the test pulse).

In hochinformativen Displays führt das Phänomen der optischen Hysterese dazu, daß bei Veränderung der Ansteuerspannung, die in der Praxis dem Testpuls des Experiments entspricht, einzelne Bildpunkte je nach ihrer Vorgeschichte schalten oder nicht schalten, wodurch sogenannte Geisterbilder auftreten.In highly informative displays, the phenomenon of optical hysteresis leads to the fact that when the control voltage changes, which in practice corresponds to the test pulse of the experiment, individual pixels switch or do not switch, depending on their history, so-called ghosting occurs.

In Fig. 2a und 2b sind als Ordinate die Intensität (in Volt; die proportional zur Transmission ist) und als Abszisse die elektrische Feldstärke (in Volt/µm) aufgetragen.2a and 2b, the ordinate is the intensity (in volts; which is proportional to the transmission) and the abscissa is the electrical field strength (in volts / μm).

Fig. 2 zeigt im Vergleich die nach der oben erläuterten Methode gewonnene Hysteresekurve eines bekannten Displays, bei dem die Elektroden durch eine Orientierungsschicht gegen den FLC isoliert sind (Fig. 2a), und eines erfindungsgemäßen Displays, bei dem zwei Orientierungsschichten aus geriebenem leitfähigen Polymer in unmittelbarem Kontakt mit dem FLC stehen (Fig. 2b). Die weitgehende Unterdrückung der Hysterese im letzteren Fall ist deutlich erkennbar.Fig. 2 shows a comparison of the hysteresis curve obtained by the method explained above of a known display, in which the electrodes are isolated from the FLC by an orientation layer (Fig. 2a), and a display according to the invention, in which two orientation layers made of rubbed conductive polymer in are in direct contact with the FLC (Fig. 2b). The extensive suppression of hysteresis in the latter case is clearly visible.

Wegen seiner guten Orientierungseigenschaft (gute planare Orientierung) und seiner hohen elektrischen Leitfähigkeit hat sich die Verwendung eines Polymers der Formel (III)

Figure imgb0021

wobei

n
= 5 oder 6 ist,

als besonders vorteilhaft für Orientierungsschichten in Displays erwiesen. Die genaue Vorgehensweise bei der Beschichtung sowie die elektrooptischen Resultate sind in Beispiel 1 erläutert.Because of its good orientation property (good planar orientation) and its high electrical conductivity, the use of a polymer of the formula (III)
Figure imgb0021

in which
n
= 5 or 6,

proven to be particularly advantageous for orientation layers in displays. The exact procedure for the coating and the electro-optical results are explained in Example 1.

Zur Erzielung hoher optischer Transparenz kann es vorteilhaft sein, statt eines reinen Polymers ein Polymer-Blend zu verwenden. So führt das Mischsystem aus dem Polymer gemäß Formel (III) und einem Poly-methacrylat der Formel (IV)

Figure imgb0022
Figure imgb0023

zu einer deutlich verbesserten optischen Transparenz. Als weitere Bestandteile für Polymer-Blends sind die oben genannten nicht leitfähigen Polymere ebenfalls besonders geeignet.To achieve high optical transparency, it can be advantageous to use a polymer blend instead of a pure polymer. This is how the mixing system performs the polymer of the formula (III) and a poly-methacrylate of the formula (IV)
Figure imgb0022
Figure imgb0023

to a significantly improved optical transparency. The above-mentioned non-conductive polymers are also particularly suitable as further constituents for polymer blends.

Die Erfindung wird durch die nachfolgenden Beispiele verdeutlicht.The invention is illustrated by the following examples.

Beispiel 1example 1

Eine 2 %ige Nitromethanlösung eines elektrisch leitfähigen Polymers mit der folgenden Strukturformel,

Figure imgb0024

wobei n gleich 5 oder 6 bedeutet,
wird durch ein Spin-Beschichtungsverfahren mit 1500 Umdrehungen/Minute auf einem 1 mm starken Glassubstrat, das vorher mit einer transparenten Elektrode versehen worden ist, 30 Sekunden lang aufgeschleudert. Das Substrat und die Schicht aus der darauf abgeschiedenen Lösung werden bei 120°C in einem Trockenschrank getempert, um das Lösungsmittel durch Destillation anzutreiben. Man erhält eine Polymerschicht mit 100 nm Schichtdicke, die anschließend mit Hilfe einer Reibemaschine jeweils 2 mal in gleicher Richtung schwach gerieben wird. Man erhält eine homogene, schwach bläuliche Polymerschicht mit 100 nm Dicke und mit einer spezifischen elektrischen Leitfähigkeit von 8,0 x 10⁻³ S/cm. Jeweils zwei der so erhaltenen und mit dem gleichen Polymer beschichteten Glassubstrate werden parallel sowie antiparallel aufeinander gelegt. Die Substrate werden mit Hilfe von Abstandshaltern zu einer Zelle mit einem Elektrodenabstand von 2,4 µm verklebt. Die Zelle wird mit der handelsüblichen, ferroelektrischen Mischung ®Felix 002 (eingetragenes Warenzeichen der Hoechst AG) gefüllt. Es wird eine gute Bistabilität gefunden. Die Zelle zeigt fast keine optische Hysterese, was durch die in Fig. 2b widergegebenen Ergebnisse belegt wird. Die optische Transparenz der Polymerschicht bei einer Wellenlänge von 550 nm beträgt ca. 50 %.A 2% nitromethane solution of an electrically conductive polymer with the following structural formula,
Figure imgb0024

where n is 5 or 6,
is by a spin coating process at 1500 revolutions / minute on a 1 mm thick Glass substrate, which had previously been provided with a transparent electrode, spun on for 30 seconds. The substrate and the layer of the solution deposited thereon are annealed at 120 ° C. in a drying cabinet in order to drive the solvent by distillation. A polymer layer with a layer thickness of 100 nm is obtained, which is then rubbed lightly twice in the same direction using a grinder. A homogeneous, slightly bluish polymer layer with a thickness of 100 nm and a specific electrical conductivity of 8.0 x 10 -3 S / cm is obtained. In each case two of the glass substrates obtained in this way and coated with the same polymer are placed on top of one another in parallel and in antiparallel. The substrates are bonded to a cell with an electrode spacing of 2.4 µm using spacers. The cell is filled with the commercially available ferroelectric mixture ®Felix 002 (registered trademark of Hoechst AG). A good bistability is found. The cell shows almost no optical hysteresis, which is confirmed by the results shown in FIG. 2b. The optical transparency of the polymer layer at a wavelength of 550 nm is approximately 50%.

Beispiel 2Example 2

Die folgenden Bestandteile werden durch Rühren in 100 cm³ γ-Butyrolacton gelöst: 1,0 g des vorstehend beschriebenen elektrisch leitfähigen Polymeren aus Beispiel 1 und 1,0 g eines Poly-methylmethacrylates der Formel (IV), das aus 50 bis 100 Monomereinheiten (1 = 50 bis 100) besteht. Die Lösung wird in gleicher Weise wie in Beispiel 1 beschrieben auf einem Glassubstrat aufgebracht, das vorher mit einer transparenten Elektrode versehen worden ist. Nach einstündigem Tempern bei 180°C ergibt sich eine Schichtdicke von 150 nm. Eine Flüssigkristallzelle mit einer 2 µm dicken Flüssigkristallschicht wird durch Ausrichtungs-Behandlung der Substrate in derselben Weise wie in Beispiel 1 hergestellt. Die Zelle wird mit der handelsüblichen ferroelektrischen Flüssigkristall-Mischung ®Felix 002 (Hersteller: Hoechst AG) gefüllt. Es wird eine gute Bistabilität gefunden. Das Flüssigkristall-Schaltelement zeigt fast keine optische Hysterese. Als optische Transparenz der Orientierungsschicht bei einer Lichtwellenlänge von 550 nm werden 77 % gemessen.The following constituents are dissolved in 100 cm 3 of γ-butyrolactone by stirring: 1.0 g of the electrically conductive polymer from Example 1 described above and 1.0 g of a poly-methyl methacrylate of the formula (IV) which consists of 50 to 100 monomer units (1 = 50 to 100). The solution is applied in the same way as described in Example 1 on a glass substrate which has previously been provided with a transparent electrode. After annealing for one hour at 180 ° C., the layer thickness is 150 nm. A liquid crystal cell with A 2 µm thick liquid crystal layer is produced by aligning the substrates in the same manner as in Example 1. The cell is filled with the commercially available ferroelectric liquid crystal mixture ®Felix 002 (manufacturer: Hoechst AG). A good bistability is found. The liquid crystal switching element shows almost no optical hysteresis. 77% are measured as the optical transparency of the orientation layer at a light wavelength of 550 nm.

Claims (6)

  1. A liquid-crystal switching and display element containing a ferroelectric liquid-crystalline medium, two electrodes, at least one polarizer, two transparent carrier plates and also at least one orienting layer, wherein at least one of the orienting layers is in direct electrical contact with the associated electrode and said orienting layer contains an electrically conductive polymer of the formula (I)
    Figure imgb0040
    in which
    R¹   = H, or straight- chain or branched alkyl or alkoxy containing 1-16 carbon atoms, or halogen,
    R²   = straight-chain or branched alkoxy containing 1-16 carbon atoms, or halogen,
    X   = S, NH,
    Y⁻   = BF - 4
    Figure imgb0041
    , PF - 6
    Figure imgb0042
    , PO 3- 4 
    Figure imgb0043
    , AsF - 6
    Figure imgb0044
    , SbCl - 6
    Figure imgb0045
    , SO 2- 4 
    Figure imgb0046
    , HSO - 4
    Figure imgb0047
    , alkyl-SO - 3
    Figure imgb0048
    , perfluoroalkyl-SO - 3
    Figure imgb0049
    , aryl-SO - 3
    Figure imgb0050
    , F⁻ or Cl⁻, and
    n   = an integer from 4 to 100,
    m   = an integer from 1 to 30.
  2. The liquid-crystal switching and display element as claimed in claim 1, wherein n is an integer from 4 to 30, m is an integer from 1 to 9 and R¹, R², X and Y have the meanings specified.
  3. The liquid-crystal switching and display element as claimed in claim 2, wherein X is a sulfur atom, Y⁻ is equal to BF - 4
    Figure imgb0051
    , PO 3- 4 
    Figure imgb0052
    , SO 2- 4 
    Figure imgb0053
    , HSO - 4
    Figure imgb0054
    , F⁻ or Cl⁻, and R¹, R², n and m have the meanings specified.
  4. The liquid-crystal switching and display element as claimed in claim 1, wherein the orienting layer contains in addition to a polymer of the formula (I) at least one nonconductive polymer.
  5. The liquid-crystal switching and display element as claimed in claim 1, wherein the orienting layer contains in addition to a polymer of the formula (I) at least one further conductive polymer.
  6. The use of electrically conductive polymers of the formula (I) as claimed in claim 1 as a component for the orienting layer or layers in liquid-crystal switching and display elements.
EP90114643A 1989-08-05 1990-07-31 Electrically conductive polymer and its use as orientation layer in liquid crystal switches and display devices Expired - Lifetime EP0412408B1 (en)

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DE3925970A DE3925970A1 (en) 1989-08-05 1989-08-05 ELECTRICALLY CONDUCTIVE POLYMERS AND THEIR USE AS AN ORIENTATION LAYER IN LIQUID CRYSTAL SWITCHING AND DISPLAY ELEMENTS
DE3925970 1989-08-05

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